The present invention relates to the compression molding of lignocellulosic materials into composite bodies, sheets and the like and more particularly to a method for preparation of particle board with polyisocyanate binder and the use of a functional polysiloxane-monocarboxylic acid or metal salt copolymer as a release agent capable of providing multiple release from the forming mold surfaces.
The molding of lignocellulosic and lignocellulosiccontaining fibers, particles or layers to form composite articles is known. Organic di - and polyisocyanates as useful binders for lignocellulose materials have been known for some time and give to particle board products increased stability and mechanical strength; see, for example, U.S. Pat. Nos. 3,428,592; 3,440,189; 3,557,263; 3,636,199; 3,870,665; 3,919,017 and 3,930,110. It is also known in the art that the isocyanate binders are mixed with the wood particles utilized as the base for the particle board. A wood chip or particle and isocyanate binder mixture is then formed into a mat and molded with pressure and temperature to the desired size or shape. Water emulsion polyisocyanate binder systems for use with lignocellulosic particles to prepare particle board are also known. A principal disadvantage of the use of isocyanates in the preparation of particle board is due to their excellent adhesive properties. Thus, isocyanate systems, either the water emulsion or the straight polyisocyanate binders, stick tenaciously to the metal caul plates which are employed to support the wood particles during transporting and the pressing or molding processes. Such poor release of the molded particle board from the caul or mold surface creates difficulty in the cleaning and automatic handling of the cauls. In order to prevent the sticking problem, external release agents have been developed and applied to the caul plates or platens or mat surface as described for example in U.S. Pat. No. 4,110,397. Other conventional release agents such as oils, waxes, polishes, silicones and polytetrafluoroethylene have been unsatisfactory as have the specialized urethane release agents including those used in structural foam applications. Another method to overcome the sticking problem has been to overlay the isocyanate bound lignocellulosic particles with a veneer of wood as shown, for example, in U.S. Pat. Nos. 3,390,110; 4,197,219 and 3,919,017 or with the use of a release paper. These methods have the disadvantage of either adding more cost to the product or of not fully utilizing the superiority of the isocyanate binder. Many of the release agents developed to date have to be applied during every composite production cycle in large quantities to be effective.